1. Technical Field
The present disclosure relates to a discrete-time analog circuit and to a transmitting device and a receiving device using the circuit.
2. Description of the Related Art
Discrete-time analog circuit configurations have been known for circuits that have high variability and that are suitable for circuit design using a fine complementary metal-oxide semiconductor (CMOS) process.
For example, S. Manetti and A. Liberatore, “Switched-Capacitor Lowpass Filter without Active Components” Electronics Letters, Vol. 16, pp. 883-885, 1980 (this document is hereinafter referred to as “Non-Patent Document 1”) discloses a discrete-time analog circuit that performs filtering on an input analog signal.
FIG. 1A is a diagram illustrating an overview of the operation of the discrete-time analog circuit disclosed in Non-Patent Document 1, and FIG. 1B is a diagram illustrating a specific example of implementation of the discrete-time analog circuit disclosed in Non-Patent Document 1. FIG. 1C is a time chart illustrating a plurality of control signals input to the discrete-time analog circuit disclosed in Non-Patent Document 1. FIG. 2 is a graph illustrating one example of a frequency characteristic of the discrete-time analog circuit in Non-Patent Document 1.
The discrete-time analog circuit in FIG. 1B performs filtering involving discrete-time analog signal processing on an input analog signal. A charge input and charge transfer between a plurality of capacitors included in the circuit in FIG. 1B realizes an infinite impulse response (IIR) filter characteristic with which the denominator is a second-degree polynomial.
When a voltage is input, a voltage-current conversion circuit is needed in addition to the configuration in FIG. 1B, and it is required that the order of an input and the order of an output be made to match each other in order to obtain a transfer function. Characteristics of a filter using the configuration in FIG. 1B have the frequency characteristic illustrated in FIG. 2.
However, of the known discrete-time analog circuit described in Non-Patent Document 1, circuitry used for charge transfer requires a large number of capacitors and uses a large number of clock signals (one type of control signal), and thus, the configuration is complicated. For example, in the simplest configuration in Non-Patent Document 1, the known discrete-time analog circuit also includes a voltage-current conversion circuit and a circuit used for charge transfer. The circuit (in FIG. 1B) used for charge transfer includes four capacitors and 12 switches. The circuit for charge transfer also uses eight types of clock signal, as illustrated in FIG. 1C. With the discrete-time analog circuit in Non-Patent Document 1, it is difficult to freely adjust in-band deviation (a level difference) in the passband.